Problem: What is the least common multiple of $4$ and $5$ ? $\text{lcm}(4, 5) = $
The least common multiple is the smallest number that is a multiple of $4$ and $5$. We know that $4 \times 5$ (or $20$ ) is a common multiple, but is it the least common multiple? Write out the multiples of $5$ until we find a number divisible by $4$. $5, 10, 15, 20$ So, the least common multiple of $4$ and $5$ is $20$.